The papers — millions of leaked confidential documents from the Mossack Fonseca law firm in Panama — identify international politicians, business leaders and celebrities involved in webs of suspicious financial transactions. The revelations have raised questions about secrecy and corruption in the global financial system.

Who was named in the leaked documents?

Among others, the documents named close associates of President Vladimir V. Putin of Russia, the father of Prime Minister David Cameron of Britain and relatives of President Xi Jinping of China and members of the Chinese Communist Party Politburo Standing Committee. Articles published by news organizations in cooperation with the International Consortium of Investigative Journalists also named King Salman of Saudi Arabia; Sigmundur David Gunnlaugsson, who resigned as prime minister of Iceland after the revelations; President Mauricio Macri of Argentina; and the soccer star Lionel Messi, one of the world’s wealthiest athletes.

What do the documents suggest that they have done?

Those prominent names were among the hundreds of people that the papers tie to thousands of offshore shell companies. Such companies can be used to shield vast wealth from tax collectors, regulators and creditors.

Many of the people named in the papers have denied in the strongest terms that they have broken any laws.

Mr. Cameron, whose father was a client of the Panamanian law firm, initially said he had not benefited from any “offshore funds,” only to confirm later that he and his wife had profited when they sold shares in an offshore trust for 30,000 pounds ($42,160) in 2010, the year he became prime minister. (The dividends they earned were declared and taxed, Mr. Cameron said.)

Were any Americans implicated?

It is not clear how many United States citizens may have been involved. So far, the documents cited in news reports have not connected any prominent American politicians or other influential Americans to Mossack Fonseca.

One reason may be that it is fairly easy to form opaque shell companies in the United States. Americans “really don’t need to go to Panama,” James Henry, an economist and senior adviser to the Tax Justice Network, told Fusion. “Basically, we have an onshore haven industry in the U.S. that is as secretive as anywhere.”

Is any of this illegal?

It is not clear whether the papers document any lawbreaking. The holding of money in an offshore company is generally not illegal by itself, but it may be done to hide criminality from prying eyes, for example, by facilitating tax evasion or money laundering.

Are there legitimate uses for foreign shell companies?

There are many valid reasons for multinational corporations, joint ventures or wealthy individuals to set up and use such companies.

For example, many countries allow land to be owned only by citizens or locally registered companies. So a foreigner seeking a retirement or vacation home would set up a local shell company to purchase the property.

A corporation establishing a joint venture in a country with a weak or corrupt legal system may want to do so through an offshore company based in a place like the British Virgin Islands or the Cayman Islands, so the venture can gain access to stronger courts and operate under more sophisticated financial laws.

They may be set up for other aboveboard financial planning purposes as well, with no intent to deceive the authorities. But experts say the secrecy provided by shell companies makes it all too easy and tempting to stray into tax evasion.